The present invention relates to carbonate polymer compositions comprising a carbonate polymer and dispersed therein a base concentrate material.
Carbonate polymers derived from reactions of dihydroxyorganic compounds, particularly the dihydric phenols, and carbonic acid derivatives such as phosgene have found extensive commercial application because of their excellent physical properties. These thermoplastic polymers are suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance and excellent electrical properties are required. It has been common industry practice to color such thermoplastic resins during the processing steps by using either color concentrates or so-called "dry color methods."
"Dry color" is the name conventionally given to colorants treated or coated with dispersing aids, such as stearic acid. Dry color can be added to virgin resin by preblending with the color pellets or by metering into the virgin pellet feedstream. Handling dry color is a dusty and dirty operation, and the degree of dispersion of the color pigment in the finished processed article is not always satisfactory. Moreover, it is difficult to achieve color uniformity in the parts produced.
As an alternative to dry color, resin processors sometimes use so-called precolored resins, supplied by the manufacturers of the resin. Precolored resin contains the desired amount of pigment already dispersed into the resin pellets in order that articles made from it have the desired shade and color.
Color concentrates are dispersions of colorants in a base resin, usually the same type of resin as the processed resin and are usually used in pellet form, at colorant concentrations of from about 5 to about 60 weight percent. The processor must either preblend the color concentrate pellets with the virgin resin pellets, or meter the color concentrate pellets into the natural resin pellet feedstream at concentrations of from about 0.2 to about 10 percent by weight. This is necessary in order to reduce the colorant concentration in the finished processed article to the desired level, usually from about 0.01 to about 3.0 weight percent.
Although there exist advantages in using additive concentrates to the compounding tasks associated with the manufacture and processing of carbonate polymer products, there are many other limitations. One such limitation is that compounding machinery must operate at relatively high temperatures, sometimes in excess of 300.degree. C. Also, the power requirements of compounding devices in processing carbon polymers are two to three times that employed in the processing of styrenic and olefinic base concentrates. Further, the fact that carbonate polymer base resins must be thoroughly dried before processing into a concentrate also adds to processing costs. In addition, trace impurities such as chloride ions, iron and the like, varying pH levels, or reactive species in the additives which can complex with phenolic species in the carbonate polymer resin can cause severe molecular weight degradation and yellowing of a concentrate made with carbonate polymer base resins.
In view of the deficiencies of conventional dry color techniques and carbonate polymer base concentrates, it would be highly desirable to provide a carbonate polymer composition comprising an alternative base concentrate without sacrificing the excellent properties of the carbonate polymer in the end product.